The embodiments described herein relate to methods and apparatus for cooling solenoids used in solenoid pumps, and more particularly, to methods and apparatus including a secondary pumping chamber to cool the solenoid coil of a solenoid pump.
Known solenoid pump assemblies are used in a variety of different applications. For example, known solenoid pump assemblies are used in a variety of vehicle applications, such as, for example, to transfer oil, fuel and/or other fluids to facilitate the operation of the vehicle. Typically, solenoid pumps or pump assemblies can be configured to receive an electrical current to cause an armature to move, thus actuating a pumping mechanism to enable transfer of fluid. In most known systems, the armature can be moved along a fixed stroke length, wherein the distance between two end-stops is fixed. Similarly stated, in normal operation, when the solenoid coil is actuated, the armature moves a fixed distance or “stroke.” The volume of fluid pumped is proportional to the stroke length and the frequency of operation.
When a solenoid pump is required to pump at high frequency (e.g., to increase the flow rate), the electromagnetic force must be generated quickly. To facilitate rapid generation of electromagnetic force, without expensive/high voltage drive electronics, it is desirable that the solenoid coil have relatively low electrical resistance. The low coil resistance, however, can lead to resistive heating, which, in turn increases the resistance of the solenoid coil, resulting in an increased voltage requirement. Thus, to maintain the desired operating voltage, the inherent electrical resistance of the solenoid coil needs to be maintained at a low value and/or additional wire turns need to be added to the solenoid coil design. Adding turns to the solenoid coil, however, increases the coil inductance, which can undesirably slow the rise of the electromagnetic force in the solenoid coil. Additionally, reducing the initial electrical resistance of the solenoid coil (i.e., to accommodate expected resistance increase) can lead to additional resistive heating during use that can exaggerate the resistance change (due to the dissipation of significant power during high frequency operation).
The increased coil resistance caused by the resistive heating can result in lower peak current during operation. To overcome the diminished performance due to the lower peak current, the pulse width and/or frequency of operation can be increased. This, however, further increases the power dissipation of the solenoid coil, and exaggerates the heating, and eventually leads to lower force values and a minimum operating voltage near or above the designs nominal operating voltage.
Accordingly, a need exists for system and methods to reduce thermally-related increases in solenoid coil electrical resistance during operation to allow the operation of the pump at high frequencies.